Monometallic rhodium-containing four-way conversion catalysts for gasoline engine emissions treatment systems

Abstract

Catalyzed particulate filters comprise three-way conversion (TWC) catalytic material, which comprises rhodium as the only platinum group metal, that permeates walls of a particulate filter. Such catalyzed particulate filters may be located downstream of close-coupled three-way conversion (TWC) composites in an emission treatment system downstream of a gasoline direct injection engine for treatment of an exhaust stream comprising hydrocarbons, carbon monoxide, nitrogen oxides, and particulates.

The invention claimed is: 
     
       1. An emission treatment system downstream of a gasoline direct injection engine for treatment of an exhaust stream comprising hydrocarbons, carbon monoxide, nitrogen oxides, and particulates, the emission treatment system comprising:
 a close-coupled three-way conversion (TWC) composite comprising a first TWC catalytic material supported on a flow-through substrate; and 
 a catalyzed particulate filter located downstream of the dose-coupled TWC composite, the catalyzed particulate filter comprising a second TWC catalytic material that permeates walls of a particulate filter, 
 wherein the second TWC catalytic material comprises rhodium as the only platinum group metal, a support, and an oxygen storage component, 
 wherein the catalyzed particulate filter has a coated porosity ranging from 75% to 98% of an uncoated porosity of the particulate filter. 
 
     
     
       2. The emission treatment system of  claim 1 , wherein the particulate filter comprises has a mean pore diameter ranging from about 13 to about 25 μm. 
     
     
       3. The emission treatment system of  claim 1 , wherein there is no layering of catalytic material on the surface of the walls of the particulate filter except optionally in areas of overlapped washcoat. 
     
     
       4. The emission treatment system of  claim 1 , wherein the coated porosity is linearly proportional to a washcoat loading of the second TWC catalytic material. 
     
     
       5. The emission treatment system of  claim 1 , wherein the second TWC catalytic material has a d90 average particle diameter in the range of from 2.5 to 8 μm. 
     
     
       6. The emission treatment system of  claim 1 , wherein the second TWC catalytic material is formed from a single washcoat composition that permeates an inlet side, an outlet side, or both of the particulate filter. 
     
     
       7. The emissions treatment system of  claim 1 , wherein a first single washcoat layer is present on the inlet side along up to a range of from 0 to 100% of the axial length of the particulate filter from the upstream end and a second single washcoat layer is present on the outlet side along up to 0 to 100% of the axial length of the particulate filter from the downstream end, and wherein at least one of the first and single washcoat layers is present in an amount of >0%. 
     
     
       8. The emissions treatment system of  claim 7 , wherein a first single washcoat layer is present on the inlet side along up to a range of from 50 to 100% of the axial length of the particulate filter from the upstream end and wherein a second single washcoat layer is present on the outlet side along up to from 50 to 100% of the axial length of the particulate filter from the downstream end. 
     
     
       9. The emission treatment system of  claim 8 , wherein the first single washcoat layer is present on the inlet side along up to a range of from 50 to 55% of the axial length of the particulate filter from the upstream end and wherein the second single washcoat layer is present on the outlet side along up to from 50 to 55% of the axial length of the particulate filter from the downstream end. 
     
     
       10. The emission treatment system of  claim 1 , wherein a single washcoat layer is present on the inlet side along up to 100% of the axial length of the particulate filter from the upstream end and there is not a washcoat layer on the outlet side. 
     
     
       11. The emissions treatment system of  claim 1 , wherein a single wash coat layer is present on the outlet side along up to 100% of the axial length of the particulate filter from the downstream end and there is not a washcoat layer on the inlet side. 
     
     
       12. The emission treatment system of  claim 1 , wherein the second TWC catalytic material is present in an amount ranging from 0.17 g/in 3  to 5 g/in 3  (10 g/L to 300 g/L). 
     
     
       13. The emission treatment system of  claim 1 , wherein the second TWC catalytic material consists essentially of rhodium, ceria or a ceria composite, and alumina. 
     
     
       14. The emission treatment system of  claim 1 , wherein the second TWC catalytic material is present in an amount ranging from 0.25 g/in 3  to 1.5 g/in 3 . 
     
     
       15. The emission treatment system of  claim 1 , wherein the oxygen storage component comprises ceria ranging from 30 wt. % to 60 wt. %. 
     
     
       16. A catalyzed particulate filter located in an emission treatment system downstream of a gasoline direct injection engine for treatment of an exhaust stream comprising hydrocarbons, carbon monoxide, nitrogen oxides, and particulates and downstream of a three-way conversion (TWC) composite comprising a first TWC catalytic material on a flow-though substrate, the catalyzed particulate filter comprising:
 a particulate filter having a wall thickness ranging from 6 mils (152 μm) to 14 mils (356 μm) and a porosity ranging from 55% to 70%; and 
 a second three-way conversion (TWC) catalytic material in an amount ranging from 0.17 g/in 3  to 5 g/in 3  (10 g/L to 300 g/L), wherein the second TWC catalytic material comprises rhodium as the only platinum group metal, 
 wherein the catalyzed particulate filter has a coated porosity that is less than an uncoated porosity of the particulate filter and a coated backpressure that is substantially the same as an uncoated backpressure of the particulate filter. 
 
     
     
       17. The catalyzed particulate filter of  claim 16 , wherein the wall thickness is 8 mils;
 the amount of the second three-way conversion (TWC) catalytic material ranges from 0.17 g/in 3  to 1.5 g/in 3  (10 g/L to 90 g/L), the second TWC catalytic material comprising rhodium as the only platinum group metal; and 
 the particulate filter has a mean pore size distribution in a range of from 13 to 25 pm. 
 
     
     
       18. A method of treating an exhaust gas comprising hydrocarbons, carbon monoxide, nitrogen oxides, and particulates, the method comprising situating the catalyzed particulate filter of  claim 16  downstream of a gasoline direct injection engine and a three-way conversion (TWC) composite comprising a first TWC catalytic material on a flow-through substrate, wherein upon operation of the engine, exhaust gas from the gasoline direct injection engine contacts the catalyzed particulate filter. 
     
     
       19. A method of making emission treatment system for a gasoline direct injection engine, the method comprising: positioning a three-way conversion (TWC) composite comprising a first TWC catalytic material on a flow-through substrate downstream of the gasoline direct injection engine; and positioning the catalyzed particulate filter downstream of the TWC composite, wherein the catalyzed particulate filter comprises a second three-way conversion (TWC) catalytic material permeating walls of a particulate filter, the particulate filter having a wall thickness ranging from 6 mils (152 μm) to 14 mils (356 μm) and a porosity in a range of from 55% to 70%; and wherein the second TWC catalytic material comprises rhodium as the only platinum group metal.